Method and System for Analog/Digital Image Simplification and Stylization

ABSTRACT

A computer program product includes instructions for a processor to perform a method of improving image structure and coherence, and/or for simplification/stylization. The method includes inputting the image, by: scanning the image; image capture using a camera; and/or image creation using a computer. Multi-channel images are converted into a single-channel image, which is separated into a first image component—the high spatial frequencies, and a second component image—the low spatial frequencies. The first and second component images are each formed by filtering to remove frequencies outside of respective upper and lower threshold frequencies. A gain multiplier is applied to the filtered first and second component images to control detail amplification. The first and second component images are each blurred at the respective upper and lower threshold frequencies. An improved stylized composite image results by subtracting the gain multiplied first component image from the gain multiplied second component image.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/250,475, filed on Apr. 11, 2014, which claims priority on U.S.Provisional Application Ser. No. 61/810,775 filed on Apr. 11, 2013, thedisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to improvements in analog/digital imageprocessing, and more particularly to a method of manipulating imagespatial frequencies to improve image structure and coherence of digitalimages.

BACKGROUND OF THE INVENTION

Images may be created by artists and technicians, using varioustechniques, from an actual physical scene, from an imaginary one that isoriginated within the mind of its creator, or from a scene generated bya computer. Still photographs of a real scene may be captured in aparticular fashion, including filtering, to achieve the artist'sexpression and evoke some emotional response in the viewer. The creationof an image by hand may include very basic methods of manipulatingperception, such as the creation of the illusion of a three dimensionalperspective view on a flat sheet, which may be accomplished using aone-point perspective, or a two-point perspective, etc. The creation ofan image by computer may be created by means such as the threedimensional rendering of mathematic scene description, e.g., a renderingof a fractal landscape or interactive virtual game world. The ability ofan artist to use a computer to manipulate an image that has beencaptured digitally to manipulate the viewer's perception, may be just aspowerful, even more powerful.

It is now known that a key basis for more complex manipulation of theway a viewer perceives an image is through the particular use of spatialfrequencies therein. In physics and mathematics, a spatial frequency isthe measure of how often a cyclic component is repeated per unit ofdistance. In wave mechanics, the spatial frequency (ν) is related to thewavelength (λ) by the formula, (ν)(λ)=1 (or, ν=1/λ). In discussions ofthe human visual system, “Spatial frequency” refers to the number ofpairs of bars imaged for a given distance on the retina, and may beexpressed as the number of cycles per degree of visual angle. One-thirdof a millimeter is a convenient unit of retinal distance because thisimage size may subtend one degree of visual angle on the retina. The useof different spatial frequencies conveys different information to aviewer about various aspects of an image. High spatial frequenciesrepresent abrupt spatial changes, such as edges formed within the image,corresponding to information regarding particular features and finedetail, whereas low spatial frequencies represent global informationrelating to overall shape, particularly its general orientation andproportions.

Visual information at different spatial frequencies or ranges of spatialfrequencies may be utilized by an artist, and may be layered one uponthe other, to convey different impressions and features, which isbecause different parts of the human eye are more perceptive to certainspatial frequencies. With an image being composed of layers of both highand low spatial frequency patterns, what is perceived by a viewer willdepend upon how the viewer looks at the image. The anatomical basis forthis phenomenon is the adaptation of a person's central vision to seeingthe finer details described by high spatial frequencies, but not thebroad, blurry patterns described by low spatial frequencies, whereas aperson's peripheral vision is the opposite, and is adapted to betterseeing the low spatial frequencies, which must be visualized outside ofyour central line of vision.

These anatomical characteristics of the human visual system explain themystery behind the smile of Leonardo Da Vinci's subject in the painting,“Mona Lisa.” The portion of her smile that appears happy (corners of thelips drawn upwards) is found within low spatial frequencies, and maythus be properly seen through a person's peripheral vision—when notlooking directly at her lips and mouth. When attempting to look directlyat Mona Lisa's smile, portions of the smile blend into the background,diminishing the appearance of a smile, leaving the viewer to questionwhether or not she is truly smiling. The same phenomenon may beexperienced with other well known works of art, such as those of theimpressionist painters, where a close and direct examination of thoseworks makes it more difficult to recognize detail because the prolificlow spatial frequencies of the work are essentially being viewed using ahigh-frequency filter, which conversely improves when viewing the workoff-center and from farther away using peripheral vision—a low-frequencyfilter.

Therefore, the methods of the present invention are directed tomanipulating both the high and low spatial frequencies of an image, toachieve certain desired simplification to, and stylization of, thatimage.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a method of manipulating thehigh and low spatial frequencies of a digital image to achieve desiredsimplification and stylization of the image.

It is another object of the invention to provide a means of separatinghigh and low spatial frequencies of an inputted image through filteringtechniques.

It is a further object of the invention to provide a means of filteringparticular bands of selective high and low spatial frequencies.

It is another object of the invention to provide a means of providingnoise reduction to accomplish the removal of non-meaningful visualinformation.

It is also an object of the invention, in one embodiment, to provide acomposite digital output of the separate, modified spatial frequencyranges, through a subtraction operation.

Further objects and advantages of the invention will become apparentfrom the following description and claims, and from the accompanyingdrawings.

SUMMARY OF THE INVENTION

The present invention is directed to a process for manipulating the highspatial frequencies and the low spatial frequencies of an image toachieve particular digital effects upon the image, including desiredsimplification and stylization of the image. The core steps of themethod may include taking a two-dimensional source image through aninput step, a frequency separation step, respective band-pass mappingsteps performed on the separated frequencies, an optional noisereduction step, and a composite output step. Additional composite stepsmay be performed, such as a final composite step where the image iscomposited with color information.

During the frequency separation step, the input image is split into twocopies—into a first copy containing the high spatial frequencies, and asecond copy containing the low spatial frequencies. The copy containingthe high spatial frequencies may be filtered in the Detail Band-pass Mapto eliminate frequencies above an upper bound frequency, and to alsoeliminate frequencies below a lower bound frequency. The band of spatialfrequencies between the two selected bounds may be subjected to a gainmultiplier to control detail amplification, and may furthermore beoffset to control light and shadow bias. A blur technique may be used atthe lower frequency bound and at the upper frequency bound, such as aGaussian blur, a Box blur, a blur filter, or other methods of achievingthe same end, which may be done optically or may be done digitally usingan algorithm. An optional noise reduction step may be performed for theremoval of random image artifacts (noise), resulting from image capturefor images derived from film or digital cameras.

The copy containing the low spatial frequencies may be subjected to acomparable Structure Band-pass Map, with respective upper and lowerfrequency bounds and an optional gain multiplier and offset. Noisereduction need not be performed on the Structure Band-pass Map becausethe lower bound frequency used is large enough that it functions as anoise reduction filter. The output from the Detail Band-pass Map and theStructure Band-pass Map may be composited together to produce the finalimage, by subtracting the Detail Band-pass Map from the StructureBand-pass Map, with an offset parameter being used to keep the finalvalue range positive. Optional post-processing steps may be performedfor noise reduction and image simplification.

The composited image creates a stylized image that resembles an artisticrendering, by emulating the artistic process of distinguishing betweenlow and high spatial frequencies, such as is achieved for comic bookillustration, for ancient Greek black figure or red figure pottery, andfor woodblock engraving illustration, where high frequency white linesare placed against low frequency areas of black, and high frequencyblack lines are placed against low frequency areas of white. Separationand manipulation of frequencies can result in better image structure,more visual coherence, a more readable image, and/or it can be used toachieve an artistic goal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating steps for performing the methodof the present invention.

FIG. 1A is an image of the highly studied portrait “Mona Lisa,” paintedby the Italian artist Leonardo Da Vinci.

FIG. 1B is the face of the Mona Lisa image of FIG. 1A, but filtered toshow the low spatial frequencies.

FIG. 1C is the face of the Mona Lisa image of FIG. 1A, but filtered toshow the high spatial frequencies.

FIG. 1D shows an example of a digital image input into the process ofthe present invention

FIG. 1E is the digital image of FIG. 1D after undergoing the detailband-pass mapping of the present invention.

FIG. 1F is the digital image of FIG. 1D after undergoing the structureband-pass mapping of the present invention.

FIG. 1G is the resultant digital image of FIG. 1E and FIG. 1F afterundergoing the composite output method of the present invention.

FIG. 2A is another example of a digital image input into the process ofthe present invention.

FIG. 2B is the digital image of FIG. 2A after undergoing the detailband-pass mapping of the present invention.

FIG. 2C is the digital image of FIG. 2B after undergoing optional noisereduction of the present invention.

FIG. 2D is the digital image of FIG. 2A after undergoing the structureband-pass mapping of the present invention.

FIG. 2E is the resultant digital image of FIG. 2C and FIG. 2D afterundergoing the composite output method of the present invention.

FIG. 2F is the resultant digital image of FIG. 2E after undergoing thethreshold output method of the present invention.

FIG. 2G is the resultant digital image of FIG. 2D after undergoing theoptional detail reduction method of the present invention.

FIG. 3A illustrates an image produced by the method of the presentinvention, whereby light and dark edges are exaggerated to revealdetails of object form, by the placement of high frequency white linesagainst low frequency areas of black, and by the placement of highfrequency black lines against low frequency areas of white.

FIG. 3B is the source image for FIG. 3A, shown prior to performing ofany of the processing step(s) of the current invention.

FIG. 4A illustrates an image produced by the method of the presentinvention, whereby disagreement between boundary edges in the detailband-pass mapping and the structure band-pass mapping creates visualeffects, such as exaggerated backlight halos.

FIG. 4B is the source image for FIG. 4A, shown prior to the performingany of the required processing step(s).

FIG. 5A illustrates a desirable graphic artifact that is created whenthe structure band-pass map is computed in image space using discretemaps, where numerical imprecision in the upper and lower bound blur mapsresults in stair-stepping of each map's values, creating the appearanceof jagged edges from the numerical errors when subtracting one map fromthe other.

FIG. 5B is the source image for FIG. 5A, shown prior to the performingany of the required processing step(s).

FIG. 6A illustrates an image that is partially in focus and partiallyout of focus in order to draw the viewer's attention to the parts of theimage that are in focus.

FIG. 6B illustrates the image of FIG. 6A after undergoing the process ofthe present invention. For out of focus areas of the image where thehigh frequency band-pass map doesn't contain any information, the lowfrequency band-pass map will be all that is shown, which replicates asimilar technique used in artist's renderings using high contrast media,where blobs of ink are used to indicate a form that is out of focus.

FIG. 7 is an illustration, by the noted illustrator Charles Dana Gibson,which contains motion (directional blurs) to show a “speed line” effect,which may be illustrated by the process of the present invention by thehigh frequency band-pass map creating edges that align with thedirection of motion.

FIG. 8A shows an image that illustrates the results of applying themethod of the present invention to an image of a scene, which containsmotion blurs.

FIG. 8B is the source image for FIG. 8A, shown prior to the performingany of the required processing step(s).

FIG. 9 is a schematic showing an exemplary computing unit capable ofbeing programmed by the instructions of the software of the presentinvention, and which may include cellular phones, personal computers,and other smart devices.

DETAILED DESCRIPTION OF THE INVENTION

For centuries—whether intentionally or intuitively—artists andillustrators have been processing visual information in a way that firstcreates a distinction between high and low spatial frequencies and thencreates images that merge or synthesize these distinctions into astylized representation of reality. This distinction between high andlow spatial frequencies may be an artistic abstraction or simplificationof the biological and/or neurological processes behind human vision. Forexample, only a small area of the retina, the fovea, is capable ofresolving high spatial frequencies. The rest of the retina sees only lowspatial frequencies. Separation and manipulation of frequencies canresult in better image structure, more visual coherence, a more readableimage, and/or it can be used to achieve an artistic goal.

An example of these effects can be seen through an analysis of Leonardoda Vinci's painting, “Mona Lisa,” which is shown in FIG. 1A. FIGS. 1B,and 1C, show the image of Mona Lisa from FIG. 1A, but filtered to onlyshow the low spatial frequencies in FIG. 1B, and the high spatialfrequencies in FIG. 1C. As described above, the portion of her smilethat appears happy (corners of the lips drawn upwards) is found withinthe low spatial frequencies illustrated in FIG. 1B, which may beproperly seen through a person's peripheral vision when looking at thecomposite image. The pursed, non-smiling lips found within the highspatial frequencies in the Mona Lisa image of FIG. 1C illustrate whatwill be visualized when attempting to look directly at Mona Lisa's smilein the composite image.

Another example of the specific use of high and low spatial frequenciesis known by comic book illustrators as an effect called the “massing ofblacks” (see e.g., “The Art Of Comic Book Inking,” by Gary Martin,rewrite by Anina Bennett, p. 9, the disclosures of which areincorporated herein by reference). Similarly, in the book “How to DrawComics the Marvel Way,” by Stan Lee and John Buscema (the disclosures ofwhich are incorporated herein by reference), the authors use black andwhite images to explain to the reader how the “massing of blacks”effects the viewer's perceptions. On page 152 of the Marvel book (1984edition), the authors show a panel image beside the comic book image,where the panel image takes the comic image and reduces it to itssimplest form, to illustrate the “crisp contrast between the stark blackand white values.” So the massing of blacks functions to clarify imagesand serves certain artistic aims, particularly by helping to “focusimportant elements in a picture by attracting the eye toward any desiredarea” and to “create dramatic moods . . . .” Therefore, the high and lowfrequencies of any image may be selectively manipulated to achieve avariety of aesthetic outcomes.

FIG. 1 contains a block diagram illustrating certain method steps of thepresent invention that may be performed to achieve particular digitaleffects to an inputted image. The core steps of the method may includetaking a two-dimensional source image 10 through an input step 15, afrequency separation step 17, respective band-pass mapping steps 20 and30 performed on the separated frequencies, an optional noise reductionstep 25, and a composite output step 40. Additional composite steps maybe performed, such as a final composite step where the image iscomposited with color information.

The source 10 may be a two-dimensional image map, the internal computerrepresentation of an image. FIG. 2A shows an example input image. Thesource image 10 may therefore be a digital image in the form of arectangular array of pixels. Each of those pixels may contain severalnumbers that represent the intensity (brightness) and the color of theimage at the pixel's location. For a grayscale digital image that uses asingle color (black), each pixel location may contain a single number.Color images that use multiple channels (e.g., the RGB image that usesRed, Green, and Blue channels) contain numbers for each channel forevery pixel location.

The source image 10 may initially be inputted using any of the followingoptions:

-   -   A) Scanned using a conventional scanner, either from a        photograph or artistic rendering (drawing, painting, collage,        etc.);    -   B) Captured using a digital video camera, still image camera, or        mobile phone;    -   C) Created on a computer or tablet by an artist who draws or        paints an image in shades of gray;    -   D) Produced by 3-dimensional design software (e.g., commercial        computer aided design and rendering software packages such as        “Modo” or “Cinema 4D”); or    -   E) Produced by real-time 3-dimensional rendering such as used in        games or game consoles (Xbox, etc.).        Note—to be informative to one of skill in the art, pseudo code        is excerpted and illustrated at appropriate sections throughout        the specification. The pseudo code to load a source image 10 is        as follows:

  pixel_width as Integer = 100; // Example value pixel_height as Integer= 100; // Example value color_image as Picture; color_image =AquireColorSourceImage(pixel_width, pixel_height);

The method of the current invention works on single channel images.Therefore, if a source image 10 contains multiple channels, a singlechannel can be used and the others may be discarded. Alternatively, thechannels may be merged to produce a single-channel grayscale image, byusing a weighting scheme. Several U.S. patents disclose a suitableconversion process, such as: U.S. Pat. No. 5,282,152 to Caviasca; U.S.Pat. No. 6,101,272 to Noguchi; U.S. Pat. No. 6,574,004 to Jacob; U.S.Pat. No. 6,774,909 to Nishio; U.S. Pat. No. 6,778,186 to Mehigan; andU.S. Pat. No. 7,945,075 to Lu, the disclosures of which are incorporatedherein by reference. Alternatively, the multiple channels may be split(i.e., separation of the R, G, and B channels) or transformed (e.g.,transformation of RGB to HSV, or RGB to HSL) into a series ofsingle-component channels, and may be processed separately, and maylater be recombined (reverse transformed).

  single_channel_image as Picture; single_channel_image =ConvertColorToGrayPicture(color_image);

The input image 15 is split into two copies at the frequency separationstep 17 into a first copy containing the high spatial frequencies, and asecond copy containing the low spatial frequencies, using proprietarysoftware, and/or using commercial software, such as Adobe® Photoshop®.(Alternatively, the separation step can be performed as part ofperforming the bandpass filtering steps discussed hereinafter).

The copy containing the high spatial frequencies may be filtered, usingproprietary software and/or commercial software, in the Detail Band-passMap 20, and may be controlled according to two required parameters andtwo other optional parameters, as follows:

-   -   Upper Bound Frequency (required): Frequencies above this ceiling        are dropped.    -   Lower Bound Frequency (required): Frequencies below this floor        are dropped.    -   Gain (optional): This multiplies the final frequency range and        controls “detail amplification.”    -   Offset (optional): This adds to/subtracts from the final        frequency range and controls “light and shadow bias.”        The resulting Detail Band-pass Map contains the spatial        frequencies between the lower bound frequency and the upper        bound frequency. The implementation presented here performs this        calculation in image space, where the parameters are expressed        as a radii parameter to a blur convolution, as follows:

  lower_high_frequency_blur_radius as Real = 1; // Example valueupper_high_frequency_blur_radius as Real = 2; // Example value

To create the Detail Band-pass Map, two low-pass maps are created byblurring copies of the input, one at the lower frequency bound and oneat the higher frequency bound. Blurring may be accomplished using aGaussian function (a bell curve), with the function being in the form:

${f(x)} = {a}^{- \frac{{({x - b})}^{2}}{2c^{2}}}$

for some real constants a, b, c, where a is the height of the curve'speak, b is the position of the center of the peak, andccontrols thewidth of the “bell,” and where e is Euler's irrational andtranscendental constant, 2.71828 . . . . Blurring may also beaccomplished using a Box blur, with Full or Partial sampling (EqualInterval, Pseudorandom or Stochastic sampling). For each pixel, a Boxblur takes a surrounding window of pixels, adds each pixel valueequally, scales the total value to be within the pixel value range, thensets the original pixel to the scaled value. Alternatively, otherfilters can be used which weight pixels unequally. A Box blur and aGaussian blur both require the integration of a lot of pixels. Forinstance, if the pixel window is 100×100, then 10000 pixels must beread. An approximation may be used whereby instead of sampling everypixel, only a fraction of the pixels are sampled, which becomerepresentative of the whole area. The locations of the sampled pixelscould be fixed (uses an equal interval, i.e., “sum every 4 pixels,”) orcould be stochastic (determined randomly).

The blur may also be accomplished through other methods, such asincremental computation (e.g., an image is repeatedly filtered with asmall blur window until the result approximates a large blur window),and/or by using a two step process of first reducing the image and usingintegration to merge many pixels into few pixels, and then enlarging theimage by interpolating from the few pixels back to many pixels, and sothe blurring method may be digital (i.e., performed by an algorithm on acomputer), or may be continuous (i.e., performed optically and thencaptured digitally):

  lower_high_frequency_detail as Picture; lower_high_frequency_detail =Smooth(single_channel_image,  lower_high_frequency_blur_radius);upper_high_frequency_detail as Picture; upper_high_frequency_detail //Smooth(single_channel_image,  upper_high_frequency_blur_radius);With the blur being performed optically, a camera may take an in focuspicture, which is used as input at step 10, then the camera lensdefocuses the same scene/image by several different amounts and eachblurred representation is used as an input to the Detail and Structureband pass steps. A further discussion of photographic unsharp maskingmay be found in U.S. Pat. No. 2,691,696 to Yule for “ElectroopticalUnsharp Masking in Color Reproduction,” and U.S. Pat. No. 4,794,531 toMorishita for “Unsharp Masking for Image Enhancement,” with thedisclosures of each being incorporated herein by reference. Although aGaussian blur produces good results, some of the other techniques arebetter when fast computation is required.

Merely to be exemplary, where the original source image in FIG. 2A is1024×811 px (pixels), the frequency ranges used to create the structurebandpass mapping of FIG. 2B may be:

-   -   upper high-spatial-frequency threshold: 3 px;    -   lower high-spatial-frequency threshold: 1 px;        and the frequency ranges used to create the detail bandpass        mapping of FIG. 2D may be:    -   upper low-spatial-frequency threshold: 512 px;    -   lower low-spatial-frequency: 16 px.        (Note: The extremely large blur radius—equal to the width of the        image—for the upper frequency range in FIG. 2D may be used to        create a particular effect—it allows the image to become “mostly        dark” or “mostly light”, depending on the brightness of the        source image. These are (spatially) global, rather than        (spatially) local, value shifts. If smaller values were used,        there would be many localized clusters of light and dark        throughout the final image rather than fewer. The use of a large        value give the entire frame a light or dark bias, much as an        artist would, when determining the overall mood or tone of an        image.).

The higher frequency lowpass map is subtracted from the lower frequencylowpass map to create an image that contains only spatial frequenciesbetween the lower and upper frequency bounds. When this calculation isperformed with Gaussian blurred images, the result is known as aDifference of Gaussians (see e.g., Konstantinos G. Derpanis, “Outline ofthe Relationship Between the Difference-of-Gaussian andLaplacian-of-Gaussian,” York University, available atwww.cse.yorku.ca/˜kosta/CompVis_Notes/DoG_vs_LoG.pdf; and Marr, D. andHildreth, E. (1980), “Theory of edge detection,” Proceedings of theRoyal Society of London, B-207, 187-217. The Detail Bandpass Mapcalculation produces negative and positive values that represent thefrequency data. The size of the values corresponds to the strength ofthe frequency information. Zero represents no frequency information. Thepseudo code implementation presented here adds a constant value afterthe subtraction to keep the value range positive.

detail_bandpass_map as Picture; detail_bandpass_map = newPicture(pixel_width, pixel_height); mid as Real = 0.5 // Pixel valuesare in the range of 0.0 to 1.0 offset as Real = 0.1; // Example valuegain as Real = 1.5; // Example value i as Integer = 0; while (i< (pixel_width × pixel_height)) // Loop through all pixels detail_bandpass_map.Pixel(i) = ((lower_high_frequency_detail.Pixel(i)  - upper_high_frequency_detail.Pixel(i)) × gain) + mid + offset;  i =i + 1; wend

FIG. 2B illustrates the results of the detail band pass mapping beingperformed upon the example input image 15 of FIG. 2A. An optional noisereduction step 25 may be performed for the removal of random imageartifacts (noise) within the image, because images that are derived fromfilm or digital cameras can contain undesirable random noise, which isan artifact resulting from image capture hardware, and which is withoutany meaningful visual information. The “signal to noise ratio” may beimproved by the application of an optional noise reduction step. Sincethe Detail Band-pass Map 20 produces negative and positive values whichrepresent the filtered frequency information and the size of the valuescorrespond to the strength of the frequency information, zero representsno frequency information. So, the Noise Reduction step may identify arange of values that are near zero, and may thereafter set them to zero.In the pseudo code implementation presented here, the previous constantvalue used to keep the range positive functions as the zero-crossingvalue and signal values below the threshold are set to this value.

  noise_lower_bound as Real = 0.25; noise_upper_bound as Real = 0.75; i= 0 while (i < (pixel_width × pixel_height))  if(detail_bandpass_map.Pixel(i) > noise_lower_bound and  detail_bandpass_map.Pixel(i) < noise_upper_bound) then    // Pixelsignal is not strong enough, treat it as noise   detail_bandpass_map.Pixel(i) = mid;  end  i = i + 1; wend

FIG. 2C illustrates the results of the optional noise reduction beingperformed upon the example Detail Band-pass Map 20 of FIG. 2B.

The second copy of the input image 15 from the frequency separation step17—the copy containing the low spatial frequencies that capture thevisual structure of the image—may be filtered in the Structure Band-passMap 30. By excluding high frequency information, this map is temporallystable with regard to changes in high frequency input, such as themotion of small objects in the scene or random noise introduced by imagecapture methods. The creation of the Structure Band-pass Map iscontrolled according to two required parameters and two other optionalparameters, as follows:

-   -   Upper Bound Frequency (required): Frequencies above this ceiling        are dropped.    -   Lower Bound Frequency (required): Frequencies below this floor        are dropped.    -   Gain (optional): This multiplies the final frequency range and        controls “detail amplification.”    -   Offset (optional): This adds to/subtracts from the final        frequency range and controls “light and shadow bias” (i.e., a        bias value is used to globally raise or lower all pixel values,        brightening or darkening the image globally, and shifting the        ratio of dark to light pixels in the final image).        The implementation presented here performs this calculation in        image space. The process of creating the Structure Band-pass Map        30 is comparable to the process of creating the Detail Band-pass        Map 20, except that different values for the frequency bounding        parameters are used:

  lower_low_frequency_blur_radius as Real = 10; // Example valueupper_low_frequency_blur_radius as Real = 20; // Example valuelower_low_frequency_detail as Picture lower_low_frequency_detail =Smooth(single_channel_image,   lower_low_frequency_blur_radius);upper_low_frequency_detail as Picture; upper_low_frequency_detail =Smooth(single_channel_image,   upper_low_frequency_blur_radius);structure_bandpass_map as Picture; structure_bandpass_map = newPicture(pixel_width, pixel_height); i = 0; while (i < (pixel_width ×pixel_height)) // Loop through all pixels structure_bandpass_map.Pixel(i) =  ((lower_low_frequency_detail.Pixel(i) -  upper_low_frequency_detail.Pixel(i)) × gain + mid + offset;   i = i +1; wendFIG. 2D illustrates the results of the detail band pass mapping beingperformed upon the example input image 15 of FIG. 2A. A Noise Reductionpass is not necessary with the Structure Band-pass Map 30 because thelower bound frequency used is large enough that it functions as a NoiseReduction filter.

Next, the output from the Detail Band-pass Map 20 and the StructureBand-pass Map 30 are composited together to produce the final image. Thecomposite operation used is subtraction, whereby the Detail Band-passMap 20 is subtracted from the Structure Band-pass Map 30. In the pseudocode implementation presented, an offset parameter is used to keep thefinal value range positive.

composite_result as Picture; composite_result = new Picture(pixel_width,pixel_height); i = 0; while (i < (pixel_width × pixel_height)) // Loopthrough all pixels  composite_result.Pixel(i) =(structure_bandpass_map.Pixel(i) * 0.5 +   detail_bandpass_map.Pixel(i); i = i + 1; wend

FIG. 2E illustrates the resultant composite image formed by the methodof the present invention, through the subtraction of the image of FIG.2B that resulted from the Detail Band-pass Map 20, from the image ofFIG. 2D that resulted from the Structure Band-pass Map 30. Although thisrepresents an image space implementation of the band pass algorithm ofthe present invention, a corresponding frequency space implementation ofthe band pass algorithm may also be performed using Fourier operations.

An additional step may also be performed, to produce a Threshold Output45, in which all of the values in the Composite Output 40 are set toeither 0 or 1, to create an image with the minimum amount of informationpossible, where the grayscale image is converted to a black and whiteimage. A threshold value is set as a parameter, and any values below thethreshold are converted to black, any values above the threshold areconverted to white. This thresholding may be used as both a datacompression step, where the image can be represented by a minimum of twovalues and anything else can be eliminated, and a simplification step.FIG. 2F illustrates the results of the Threshold Output 45 method of thepresent invention.

An optional Post-Processing step 50 for detail reduction may also beperformed, in which the removal of visually insignificant image detailmay serve to achieve image simplification. The output image may besimplified by an optional Noise Reduction and Image Simplification stepusing a “connected component removal” process. In this process, eachcolor value in the composite image output 40 or the threshold output 45is compared to its neighbor. Values with similar neighbor values areconnected to form regions of similar value. The number of values in aregion corresponds to the area of the region. Regions with an area belowa defined threshold are removed. This threshold value forPost-Processing step 50 is different from the threshold used in step 45.In this case it does not represent a pixel's intensity, but a region orpixel grouping's area. i.e., a group of 6 white pixels has an area of 6pixels. Area and Pixels have a 1:1 relationship. So if the threshold forgroupings that needed to be removed was 10 pixels, then a grouping of 6pixels would fall below that threshold and would be removed from theimage. “Region removal” can be performed by automatic in-filling (i.e.,filling in missing data), or if applied to Threshold Output (450), bybit-flipping. In practice, small area values represent noise whilelarger area values represent image details. Removal of small regionsconstitutes Noise Reduction. Removal of larger regions constitutes ImageSimplification. In general, in-filling may be accomplished by using aweighted average of pixel values of the neighboring pixels.

It should be noted that additional composite steps may also be performedafter for Post-Processing step 50, such as a final composite step wherethe image is composited with color information, depending upon such aneed to process and stylize color information.

The compositing of the Detail Band-pass Map 20 and the StructureBand-pass Maps 30 into the Composite Output 40 creates a stylized imagethat resembles an artistic rendering by emulating the artistic processof distinguishing between low and high spatial frequencies. This type ofrendering is an elegant way to encode just the visual information thatwould be relevant to a viewer. The process has several identifiablevisual elements that are considered useful properties of many artisticrendering techniques.

For example, artists often exaggerate light and dark edges to revealdetails of object form. In the case of high contrast imagery (such ascomic book illustration, ancient Greek black figure or red figurepottery, and woodblock engraving illustration), high frequency whitelines are placed against low frequency areas of black, and highfrequency black lines are placed against low frequency areas of white.This is illustrated in FIG. 3, which was produced by using thehereinabove described method.

Disagreement between boundary edges in the Detail Band-pass Map 20 andStructure Band-pass Map 30 automatically creates visual effects such asexaggerated backlight halos, as seen in FIG. 4.

A desirable graphic artifact is created when the Structure Band-pass Map30 is computed in image space using discrete maps: Numerical imprecisionin the upper and lower bound blur maps results in banding (orstair-stepping) of each map's values. Numerical errors when subtractingone map from the other introduce jagged edges that appear to be made byan artist filling in the dark areas with brush and ink, as seen in FIG.5. Brush and ink illustrators use a technique of filling in large areasof black (such as areas of low frequency detail) with quick brushstrokes of ink. The tapered leading and trailing edges of the brushstroke soften hard transitions by introducing a cross-hatch effect.

If the high frequency band-pass map doesn't contain any information,then the low frequency band-pass map will be all that is shown. Asimilar technique is used in artist's renderings using high contrastmedia, such as pen and ink, where blobs of ink are used to indicate formthat is out of focus, as seen in comparing FIGS. 6A and 6B.

If the source image contains motion (directional) blurs, then the highfrequency band-pass map will create edges that align with the directionof motion. This is visually similar to “speed line” effects used byillustrators and animators, as shown by the illustration in FIG. 7, bythe noted illustrator Charles Dana Gibson.

FIG. 8A shows the result of applying the method described herein to animage of a static scene, taken when the camera was held steady. FIG. 8Bshows the result of applying the method to an image of the same scenewhere the camera was moved during the exposure, resulting in motionblur.

The separation of images into structure and detail components is aneconomical way to encode images. The Detail Band-pass Map 20, theStructure Band-pass Map 30, the Composite Output 40, or Threshold Output45 may produce sparse visual representations that work well with digitalimage compression algorithms.

Separation of the image into structure and detail components providestemporal stability in the structure component. When processing videoframes or a sequence of still images that change over time, the lowerbound frequency cutoff of the Structure Band-pass Map 30 removes highfrequency information. In normal image or frame sequences of people,environments or nature captured from the real world by cameras, highfrequency visual information changes more rapidly than low frequencyvisual information. The Structure Band-pass Map 30 component providesspatial continuity over time, which has two effects:

-   -   a. Less visual distraction: “Jumping” and “Jittering” of        irrelevant visual information is filtered out; and    -   b. Better video compression: Digital video compression        algorithms produce more efficient encoding because these        compression algorithms look for, and encode, temporally stable        visual information.

Software of the present invention may run on a computer, a server, atablet, a cell phone, or other smart device, so a description of such anaccessorized exemplary computer system is hereinafter disclosed, eventhough a particular embodiment may not require all of the describedcomponents. Exemplary computer system 200 is shown schematically in FIG.9, and which may comprise computing unit 201 interacting with externalperipherals 202, such as a separate touch screen display 244, andinteracting with network resources 203, including use of the internet261, and other computers, which may be first and second laptop computers262/263, a tablet, a smart phone, etc.

The computing unit 201 may include a data bus 224 for communicatinginformation across and among various parts of computing unit 201, and acentral processing unit, which may be a microprocessor (hereinafter“processor” or “CPU”) 222 coupled with a bus 224 for processinginformation and performing other computational and control tasks.Computing unit 201 may also include a volatile storage 225, such as arandom access memory (RAM) or other dynamic storage device, coupled tobus 224 for storing various information as well as instructions to beexecuted by processor 222. The volatile storage 225 may also be used forstoring temporary variables or other intermediate information duringexecution of instructions by processor 222. Computing unit 201 mayfurther include a read only memory (ROM) or an erasable programmablememory (EPROM) 227 or other static storage device coupled to bus 224 forstoring static information and instructions for processor 222, such asbasic input-output system (BIOS), as well as various systemconfiguration parameters. A persistent storage device or non-volatilememory 226, such as a magnetic disk, optical disk, or solid-state flashmemory device may be provided and may be coupled to bus 224 for storinginformation and instructions.

Computing unit 201 may be coupled via bus 224 to an integral display221, possibly a touch-screen display, for use in displaying informationto a user. If desired, computing unit 201 may be coupled via bus 224 toan external display screen 244. An external input device 243 (e.g., astandard keyboard) may be coupled to bus 224 for communicatinginformation and command selections to processor 222. A cursor controldevice 242, such as a mouse, a trackball, or cursor direction keys, maybe used for communicating direction information and command selectionsto processor 222 and for controlling cursor movement on display 244. Anexternal storage device 241 may be connected to the computing unit 201via bus 224 to provide an extra or removable storage capacity for thecomputing unit 201, which may be used to facilitate exchange of datawith other computer systems.

Some of the techniques herein may be performed by computing unit 201 inresponse to processor 222 executing one or more sequences of one or moreinstructions contained in the volatile memory 225. Execution of thesequences of instructions contained in a non-transitory memory may causeprocessor 222 to perform the process steps described herein. Inalternative embodiments, specific hard-wired digital circuitry may beused in place of, or in combination with, software instructions toimplement the invention.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to processor 222 forexecution. The computer-readable medium is just one example of amachine-readable medium, which may carry instructions for implementingany of the methods and/or techniques described herein. Various forms ofcomputer readable media may contain one or more sequences of one or moreinstructions for the processor 222 to execute, including non-volatilemedia (storage device 226), and volatile media (storage device 225).Common forms of computer-readable media include, for example, a floppydisk, a hard disk, magnetic tape, or any other magnetic medium, aCD-ROM, a flash drive, and a memory card.

The computing unit 201 may thus also include a communication interface,such as network interface card 223 coupled to the data bus 222.Communication interface 223 may provide a two-way data communicationcoupling to a network link that may be connected to a local network. Forexample, communication interface 223 may be an integrated servicesdigital network (ISDN) card or a modem to provide a data communicationconnection to a corresponding type of telephone line, or it may be alocal area network interface card (LAN NIC) to provide a datacommunication connection to a compatible LAN.

Network link 223 also typically provides data communication to othernetwork resources. For example, the network link may provide aconnection over the internet 261 to the world-wide-web. Thus, thecomputing unit 201 can access resources located anywhere using theInternet 261. Also, the computing unit 201 may also be accessed by, orcommunicate with, other computers (e.g. 262-263), or another smartdevice (e.g., smartphone 264), generally with permission, and which maybe located anywhere with access to the internet 261.

The examples and descriptions provided merely illustrate a preferredembodiment of the present invention. Those skilled in the art and havingthe benefit of the present disclosure will appreciate that furtherembodiments may be implemented with various changes within the scope ofthe present invention. Other modifications, substitutions, omissions andchanges may be made to the preferred embodiment without departing fromthe spirit of this invention.

We claim:
 1. A computer program product, for use in a method ofmanipulating the spatial frequencies of a multichannel image, saidcomputer program product comprising a non-transitory computer-readablestorage medium storing instructions that, when executed on a processor,cause the processor to manipulate the image according to said method,said method comprising: inputting the multichannel image; converting themultichannel image into a single channel image; separating the singlechannel image into a first component image comprising the high spatialfrequencies, and a second component image comprising the low spatialfrequencies; filtering said first component image for filtering outfrequencies above an upper high-spatial-frequency threshold, and forfiltering out frequencies below a lower high-spatial-frequencythreshold; blurring said filtered first component image at each of saidupper high-spatial-frequency threshold and said lowerhigh-spatial-frequency threshold; filtering said second component imagefor filtering out frequencies above an upper low-spatial-frequencythreshold, and for filtering out frequencies below a lowerlow-spatial-frequency threshold; and producing a composite image bysubtracting the filtered and blurred first component image from thefiltered second component image.
 2. The computer program productaccording to claim 1, wherein said method further comprises using anoffset parameter for keeping a value range of said composited imagepositive.
 3. The computer program product according to claim 1, whereinsaid blurring comprises a blurring technique from the group of blurringtechniques consisting of: a Gaussian blur, a Box blur, a blur filter,and optical blurring.
 4. The computer program product according to claim1, wherein said method further comprises said filtered first componentimage being offset to control light and shadow bias.
 5. The computerprogram product according to claim 1, wherein said method furthercomprises performing a noise reduction step for removing random imageartifacts from said separated first component image.
 6. The computerprogram product according to claim 1, wherein said method furthercomprises setting all of the values in the composite image to either 0or 1, for converting the composited image to a black and white image, bysetting a threshold value, and by converting any values in the compostedimage below the threshold to black, and converting any values in thecomposted image above the threshold to white.
 7. The computer programproduct according to claim 6, wherein said method further comprisessimplifying said black and white image in a component removal process bycomparing a value in the black and white image to its neighbor value;wherein a value with two or more similar neighbor values are connectedto form regions of similar value; and wherein a region with an areabelow a defined threshold is removed.
 8. The computer program productaccording to claim 1, wherein said method further comprises applying again multiplier to said filtered first component image and to saidfiltered second component image to control detail amplification.
 9. Aprocessor-implemented method, for manipulating the spatial frequenciesof an image, said method comprising the following steps implemented byone or more processors: inputting the image; converting the image into asingle-channel image; separating the single-channel image into a firstcomponent image comprising high spatial frequencies, and a secondcomponent image comprising low spatial frequencies, said separatingcomprising: filtering the single-channel image for filtering outfrequencies above an upper high-spatial-frequency threshold and forfiltering out frequencies below a lower high-spatial-frequencythreshold, to produce said first component image; filtering thesingle-channel image for filtering out frequencies above an upperlow-spatial-frequency threshold, and for filtering out frequencies belowa lower low-spatial-frequency threshold, to produce said secondcomponent image; blurring at least a portion of said first componentimage; and producing a composite image by subtracting the blurred firstcomponent image from the second component image.
 10. Theprocessor-implemented method according to claim 9, wherein said methodfurther comprises using an offset parameter for keeping a value range ofsaid composited image positive.
 11. The processor-implemented methodaccording to claim 9, wherein said blurring comprises a blurringtechnique from the group of blurring techniques consisting of: aGaussian blur, a Box blur, a blur filter, and optical blurring.
 12. Theprocessor-implemented method according to claim 9, wherein said methodfurther comprises said filtered first component image being offset tocontrol light and shadow bias.
 13. The processor-implemented methodaccording to claim 9, wherein said method further comprises performing anoise reduction step for removing random image artifacts from saidseparated first component image.
 14. The processor-implemented methodaccording to claim 9, wherein said method further comprises setting allof the values in the composite image to either 0 or 1, for convertingthe composited image to a black and white image, by setting a thresholdvalue, and converting any values in the composted image below thethreshold to black, and converting any values in the composted imageabove the threshold to white.
 15. The processor-implemented methodaccording to claim 14, wherein said method further comprises simplifyingsaid black and white image in a component removal process by comparing avalue in the black and white image to its neighbor value; wherein avalue with two or more similar neighbor values are connected to formregions of similar value; and wherein a region with an area below adefined threshold is removed.
 16. The processor-implemented methodaccording to claim 9, wherein said method further comprises applying again multiplier to said filtered first component image and to saidfiltered second component image to control detail amplification.
 17. Theprocessor-implemented method according to claim 9, further comprisingblurring said at least a portion of said first component image byblurring said first component image at each of said upperhigh-spatial-frequency threshold and said lower high-spatial-frequencythreshold;
 18. The processor-implemented method according to claim 9,further comprising performing said converting, separating, blurring, andcompositing steps in image space.
 19. The processor-implemented methodaccording to claim 9, further comprising performing said converting,separating, blurring, and compositing steps in frequency space using oneor more Fourier operations.